1. Field of the Invention
This invention relates to a process for regenerating crystalline aluminosilicate zeolite catalysts which have been used to promote conversion of methanol and/or methyl ether to light olefins.
2. Description of the Prior Art
A remarkable growth in the production of synthetic fibers, plastics and rubber has taken place in recent decades. Such growth, to a large extent, has been supported and encouraged by an expanding supply of inexpensive petroleum raw materials such as ethylene and propylene. However, increasing demand for these light olefins has, from time to time, led to periods of shortage, either due to a diminished supply of suitable feedstocks or to limited processing capacity. In any event, it is now considered highly desirable to provide efficient means for converting raw materials other than petroleum to light olefins.
One such non-petroleum source of light olefins is coal-derived methanol and methyl ether. In this respect, it is known that methanol or methyl ether can be catalytically converted to olefin-containing hydrocarbon mixtures by contact under certain conditions with particular types of crystalline zeolite catalyst materials. U.S. Pat. No. 4,025,575, issued May 24, 1977, to Chang et al and U.S. Pat. No. 4,083,889, issued Apr. 11, 1978 to Caesar et al, for example, both disclose processes whereby methanol and/or methyl ether can be converted to an olefin-containing product over a ZSM-5 type (constraint index 1-12) zeolite catalyst. ZSM-5, in fact, converts methanol and/or methyl ether to hydrocarbons containing a relatively high concentration of light (C.sub.2 and C.sub.3) olefins with prolonged catalyst lifetime before catalyst regeneration becomes necessary.
It is also known that other types of zeolite catalysts can be used to convert methanol and/or methyl ether to olefin-containing hydrocarbon products containing even higher proportions of light olefins than can be realized by methanol/methyl ether conversion over ZSM-5. For example, U.S. Pat. Nos. 4,079,095 and 4,079,096, both issued Mar. 14, 1978, to Givens, Plank and Rosinski, disclose that zeolites of the erionite-offretite type, and especially ZSM-34, can usefully be employed to promote conversion of methanol and/or methyl ether to products comprising a major amount of C.sub.2 and C.sub.3 light olefins. However, while erionite-offretite type catalysts are highly selective to light olefins production, such smaller pore zeolites tend to age rapidly in comparison to ZSM-5 when used for methanol/methyl ether conversion.
Aged methanol/methyl ether conversion catalysts of this type can, of course, be regenerated in conventional manner by contacting the catalyst at elevated temperature with an oxygen-containing gas such as air to effect controlled burning of coke from the deactivated catalyst. While such a conventional regeneration procedure can restore catalytic activity diminished by coke formation on the catalyst during methanol/methyl ether conversion, regeneration in this manner must be conducted in the absence of organic reactants and preferably in a separate regeneration zone which is remote from the methanol/methyl ether conversion zone. Furthermore, catalyst regeneration by controlled burning of coke produces water and carbon dioxide, and water at high temperatures can permanently destroy the structure of the zeolite catalyst and thus can actually diminish catalytic activity in some instances. There is, therefore, a continuing need to develop additional catalyst regeneration procedures which can be employed to restore the diminished activity of the zeolite-based catalysts which have been used to promote the conversion of methanol and/or methyl ether to hydrocarbon products selectively enriched in light olefins.
Accordingly, it is an object of the present invention to provide an improved process for regenerating those zeolite based catalysts which promote conversion of methanol and/or methyl ether to olefin-containing products with high selectivity to production of light olefins.
It is a further object of the present invention to provide such a regeneration process wherein catalyst can be regenerated either in the presence or absence of the methanol/methyl ether organic reactants and either in or outside of the methanol/methyl ether conversion reaction zone.
It is a further object of the present invention to provide such a catalyst regeneration procedure which does not produce by-products such as water that are potentially damaging to the catalyst structure or activity.